Connector for coupling a microwave coaxial circuit to a microstrip printed circuit

ABSTRACT

A COUPLING APPARATUS FOR CONNECTING A COAXIAL LINE TO A FLAT LINE CONFIGURATION BY MEANS OF A COAXIAL COUPLING INCLUDING A TAPERED PIN OF A PARTICULAR CONFIGURATION PROVIDING COLINEAR ALIGNEMENT OF THE COAXIAL LINE AND THE FLAT LINE CONFIGURATION, OPTIMAL IMPEDANCE MATCHING AND EXTREMELY BROAD BAND PERFORMANCE.

Jan. 5; 1971 S. 8; LEHRFELD CONNECTOR FOR COUPLING A MICROWAVE COAXIAL CIRCUIT. TO A MICROSTRIP PRINTED CIRCUIT Filed Feb.'29, 1968 145.14 vs. FREQ.

FIG-.2"

45 INVENTOR.

SANFORD s. LEHRFEYLD ATTQRNEYS United States Patent 0 U.S. Cl. 333-34 10 Claims ABSTRACT OF THE DISCLOSURE A coupling apparatus for connecting a coaxial line to a flat line configuration by means of a coaxial coupling including a tapered pin of a particular configuration providing colinear alignment of the coaxial line and the fiat line configuration; optimal impedance matching and extremely broad band performance.

The present invention relates to high frequency circuits especially in the microwave range and more particularly to' a novel coupling means for connecting a coaxial line to a non-symmetrical round plane or microstrip line while providing colinear alignment of the connected elements, extremely broad band performance not heretofore obtainable and optimal match of the voltage standing wave ratio.

The development of printed circuit technology and especially monolithic and integrated circuit technolog has grown quite considerably in the past few years and the range of application of such circuitry has logically been extended into the microwave field. However, in order to adapt such circuitry for use in microwave apparatus it has been necessary to provide means for coupling conductive members typically used for carrying microwave signals, i.e. coaxial cable, to transmitting, receiving or other applicable circuits of the printed circuit type.

There are presently available connectors capable of coupling coaxial cable to printed circuits of the symmetrical type, which circuits are comprised of a strip line imbedded between two insulating sheets on the outer surfaces of which are provided a conductive surface. The connector is provided with a conductive member which couples the central conductor of the coaxial line to the strip lines sandwiched between the two insulating members. While such conventional arrangements for coupling coaxial cable to such strip line, also commonly referred to as asymmetrical microstrip lines, no connectors are presently available for coupling axial lines to an asymmetrical microstrip circuit comprised of a microstrip line for coupling to the connector spaced from a single ground plane by a sheet or slab of insulation.

The present invention provides a novel connector, also referred to as a chip launcher, for use with asymmetrical ground plane structures which provides for in-line connection, extremely broad band frequency response and has an extremely low voltage standing wave ratio (VWSR) over the operating range. In addition to providing extremely broad band frequency response for nonsymmetrical microstrip circuitry, it has been found that the coupled provides extremely good frequency response at frequencies well above the range attainable with conventional connectors employed in symmetrical microstrip circuits, which circuits have a very high permittivity (e) to provide for low losses at microwave frequencies.

The present invention is comprised of a mounting plate having a hollow cylindrical section projecting from one surface thereof and being threaded t0 threadedly engage the terminal member of a coaxial line. The hollow interior of the cylindrical projection is fitted with an annular 3,553,607 Patented Jan. 5, 1971 shaped insulating member which positions and supports a conductive pin arranged colinear with the longitudinal axis of the insulating member and. the threaded cylindrical projection. The pin is provided with a slot at one end thereof for coupling to the coaxial cable and its opposite end is tapered to form a frusto-conical section. Extending beyond the frusto-conical section is a short ta b integrally formed with the pin and having at least one fiat surface for providing firm electrical engagement with a narrow elongated strip conductor.

The strip conductor is provided on one surface of an insulating substrate having a ground plane provided on the opposite surface thereof. The substrate carrying the conductive surfaces is securely mounted to the mounting plate which is provided with a plurality of openings for receiving threaded fastening members which threadedly engage the substrate. If desired, a conductive ground plane surface may be positioned between a second insulating substrate for engagement with the mounting plate.

The tab provided on the conductive pin extends beyond the surface of the mounting plate in a direction toward the strip conductor.

Firm electrical engagement between the tab of the conductive pin and the strip conductor is assured through providing an insulating member positioned above the tab and secured to the mounting plate by suitable fastening members which assure firm electrical contact between the tab and the strip conductor.

The length and taper of the conductive pin frustoconical portion assures excellent impedance matching between the coaxial line and the microstrip transmission line. It has been found that excellent impedance matching and a voltage standing wave ratio (VSWR) of no greater than 1.10 is obtained over an operating frequency range from DC. to 12 gigacycles. In cases where electrical contact requirements are extreme, necessitating a solder con nection between the tab and the strip conductor, the insulating pressure plate may be omitted without in any way etfecting the impedance match and VSWR over the entire operating frequency range. The provision of an in-line arrangement between the coaxial line and the microstrip assembly greatly simplifies system design and packaging. Heretofore, impedance matching between the coaxial and the microstrip assemblies over the aforementioned operating frequency range or an portion of the operating frequency range necessitated the provision of providing additional components in the microstrip circuitry. The arrangement of the conductive pin completely eliminates the necessity for such impedance matching techniques.

Launchers employed for use with symmetrical ground planes have been found to provide suitable operation up to a maximum operating frequency of 10 gigacycles. Prior techniques employed in launchers for use with microstrip assemblies have been capable of providing satisfactory operation up to a maximum frequency of only 3 gigacycles. There is no necessity for providing a compensation hole in the chip launcher and the sharp line of demarcation between the tapered portion and the tab is substantially exactly aligned with the line of demarcation between the coaxial and microstrip assemblies which further contributes to the excellent impedance matching and low VSWF obtained over an extremely broad range of operating frequencies.

It is therefore one object of the present invention to provide a novel means for coupling a coaxial line to a microcircuit while obtaining excellent impedance matching therebetween and an extremely low VSWR over a broad operating frequency range not heretofore capable of being obtained through the use of conventional devices.

Another object of this invention is to provide a novel chip launcher for use in coupling coaxial lines to a nonsymmetrical ground plane or microstrip line through the use of a launcher assembly including a taper conductive pin having a configuration assuring excellent impedance matching over the operating frequency range.

Still another object of this invention is to provide a novel launcher for use in coupling coaxial lines to microcircuits comprising a cylindrically shaped conductive member adapted for threaded engagement with a terminal coupling of a coaxial line and having an integrally formed flange connector to enable in-line securement with the microcircuit assembly.

Still another object of this invention is to provide a novel launcher for use in coupling coaxial lines to microcircuits comprising a cylindrically shaped conductive member adapted for threaded engagement with a terminal coupling of a coaxial line and having an integrally formed flange connector to enable in-line securement with the microcircuit assembly and further comprising a coaxially mounted conductive pin positioned within the cylindrically shaped connecting member having a tapered section near one end thereof terminating in a short tab extending beyond the surface of the flange connector confronting the microstrip circuit for making electrical connection with the strip conductor of the non-symmetrical microstrip transmission line.

Another object of this invention is to provide a novel launcher for use in coupling coaxial lines to microcircuits comprising a cylindrically shaped conductive member adapted for threaded engagement with a terminal coupling of a coaxial line and having an integrally formed flange connector to enable in-line securement with the microcircuit assembly and further comprising an insulating mounting slab for in-line securement to the flange connector providing firm electrical contact between the conductive pin of the launcher and the strip conductor of the microstrip transmission line.

Yet another object of this invention is to provide a novel launcher for coupling coaxial lines to non-symmetrical microstrip transmission lines including a coaxially aligned conductive pin having a configuration at the end engaging the microstrip circuitry which provides excellent impedance matching and extremely low VSWR over an extremely broad operating frequency range.

These and other objects of the present invention will become apparent when reading the accompanying description and drawings in which:

FIG. 1 is a perspective view showing a launcher of the present invention coupled to a microstrip assembly.

FIG. '2 shows a sectional view of the launcher of FIG. 1.

FIG. 3 shows an end view of the launcher of FIG. 1 looking in the direction of arrows A-A of FIG. 2.

FIGS. 4a-4c show an end view, a partial side view and an opposite end view, respectively of the conductive pin included in the launcher assembly.

FIG. 5 is a plot showing the variation in VSWR versus frequency for the launcher of FIGS. 1-4.

FIGS, 6 and 7 are partially sectionalized views showing alternative embodiments of the launcher of FIG. 1.

As shown in FIGS. 1-3, the launcher 10 of the present invention is comprised of a metallic flange connector 11 and an integrally formed cylindrical portion 12 having a central opening 12a communicating with the flange connector 11 which increases to an opening of slightly wider diameter, portion 12b, toward the right-hand end with reference to FIG. 2. The threaded portion 120 is adapted to threadedly engage a female socket (not shown) of a coaxial cable (also not shown).

A cylindrically shaped dielectric head 13 is force-fitted into the opening portion 12a and is provided with a central opening 13a whose longitudinal axis 14 is colinear with the longitudinal axis of threaded member 12.

A conductive pin 15 of substantially cylindrical shape is force-fitted into the opening 13a and has its longitudinal axis colinear with the phantom line 14. In order to assure suitable force-fitting of the elements 12, 13 and 15 relative to one another, pin 15 may be provided with an annular groove 15a. A small radially aligned hole 16 may be drilled or otherwise provided in members 12 and 13. The radially aligned hole 16 and the annular groove 15a is then filled with a suitable plastic material having good dielectric properties such as, for example, an epoxy. This rigidly positions the elements 11, 12 and 13 relative to one another to prevent any longitudinal movement of each part with respect to the other. Alternatively, the pin member 15 may be force-fitted into the dielectric sleeve and the sleeve in turn, may be force-fitted Within the threaded member 12.

As shown in FIGS. 4a-4c, the right-hand end of pin 15 is provided with a horizontally aligned slot 15b for coupling to the central conductor of a coaxial line (not shown). The horizontally aligned slot 15b further communicates with a cylindrical shaped opening 15 for receiving a slotted pin 45 (see FIG. 4b) which is force-fitted into cylindrical shaped opening 15c. This pin serves as a female jack for connection with the central conductor of a male connector.

The left-hand end of conductive pin 15 is tapered to form a frusto-conical portion 15c which ultimately terminates into a flat tab portion 15d. The frusto-conical portion abruptly ends at a flat surface 15c.

As can clearly be seen from FIG. 2, the flat surface 15e defining the termination of portion 15c, is coplanar with the surface 11a of flange connector 11 which confronts the microstrip assembly. The tab 15d can thus be seen to extend completely beyond opening 13a and to the left of surface 11a relative to FIG. 2.

The flange connector 11 is provided with a pair of apertures 16a and 16b for receiving threaded fastening membore 17 (only one of which is shown in FIG. 2). These fasteners threadedly engage a dielectric substrate 21 hav a high permittivity (e) adaptable for use in microstrip applications.

The top surface 18a of substrate 18 (see FIG. 1) has deposited thereon a strip conductor 19 which may be formed through the use of either thin fllm or thick film techniques. The strip conductor may be either etched, printed or vacuum deposited and may further be machined or custom ground, depending upon the needs of the particular user. The actual configuration of the circuitry or conductive line provided upon the surface 18a is likewise dependent upon the particular applications and may, for example, be circuitry such as active elements, passive elements, amplifiers, mixers, converters and so forth. While the actual circuit configuration deposited or otherwise formed on surface 18a may take any form, at least a portion thereof should include a microstrip conductor 19a, shown in FIG. 2, arranged in an in-line fashion with the launcher 10 and especially with the tab 15d of conductive pin 15. The high epsilon (e) substrate has deposited, or otherwise formed on its undersurface, a conductive ground plane 20 forming, together with the strip conductor 19a, a non-symmetrical ground plane also commonly referred to as a microstrip line. The slab 18 may have further secured thereto a second high-dielectric slab 21 which is aflixed to the conductive ground plane 20 and which receives the threaded fastener 17 to secure the microstrip assembly to the flange connector 11. The openings 16a and 16b receiving the threaded fasteners 17 are preferably of slightly larger diameter than the threaded portion of the fasteners to enable positioning of the conductive portion 19a immediately beneath the tab 15d so as to assure firm electrical contact between these two members. Once the appropriate positioning is obtained, the threaded fastener 17 may then be tightened to securely fasten the microstrip line assembly to the flange connector.

In order to further assure firm electrical contact between tab 15d and microstrip line portion 19a, as Plexi glas slab 22 having a substantially flat undersurface 22a is firmly pressed against the upper surface of tab 15d to provide firm electrical engagement between members 15d and 19a. The flange connector 11 is further provided with a pair of opening 16c and 16d for receiving fastening members 23 (only one of which is shown in FIG. 2) which freely pass through the associated openings 16c and 16d to threadedly engage slab 22. As was previously mentioned, the openings 16c and 16d are preferably of greater diameter than the threaded portion of fasteners 23 so as to enable slab 22 to be pressed into firm pressure contact with tab 15d in order to provide good electrical contact between elements 19a and 15d. The fasteners 23 may then be tightened to maintain the desired firm pressure contact.

In addition to the rather precise physical dimensions required of the interconnecting elements such as, for ex ample, providing accurate coupling between pin 15 and the coaxial line assembly (not shown) and the tab 15d and the strip line conductor 19a to assure excellent electrical contact therebetween, it is of equal importance to provide for good impedance matching between the coaxial assembly and the microstrip line assembly such that the impedance matching will remain constant over a broad operating frequency band, as well as providing an optimum match of the VSWR (voltage standing wave ratio) over the aforesaid operating frequency range.

The above characteristics are assured by forming the tapered portion 150 of pin 15, taking fully into account the optinal environments to which the assembly may be exposed. For example, an excellent impedance match over the broad operating frequency band is obtained regardless of whether the slab 22 is employed or removed. In certain applications, electrical contact between tab 15d and conductive line portion 19a is satisfacory so as to avoid the need for the slab. In such cases no modification need be made to the pin taper since its optimal design is already accounted for the use of the assembly in the absence of the slab. In applications where slab 22 is required to provide the minimum required electrical con tact between elements 15d and 19a, the addition of slab 22 effects the impedance characteristics of the assembly. This change in impedance characteristics will, however, have no effect whatsoever upon the impedance matching and optimal match of the VSWR as a result of the manner in which the tapered portion 15c has been formed. It has been found through exhaustive experimentation and testing that the assembly of FIG. 2, whether used with or without slab 22, provides excellent impedance matching between the coaxial assembly and the microstrip line over an operating frequency range extending from DC. to 12 gigacycles. Equally good results are obtained when slab 22 is added to the structure.

In addition to the angle of the taper and the length of the taper, it should further be noted that the taper ends abruptly at surface 15e which constitutes the demarcation line between the coaxial line and microstrip assemblies which has been found to greatly simplify and enhance the impedance matching of the assemblies. It has also been found to be extremely advantageous to form conductive pin 15 from a solid member and to machine the slot 1512, the taper 15c and the tab 15d, thereby providing a solid integral pin member.

The angle of the taper lies within a range from 8 to 36 and is preferably 11 /2 While the length of the taper L lies within the range from to 40 mils and the thickness T of the taper lies within the range from 0275" to 0405". The tab d should have a length L lying in the range from .030" to .040. The thickness of tab 15d lies within the range from 4 to 10 mils and is preferably 6 mils thick. The width W of tab 15d lies within the range from 10-22 mils and preferably should be mils. With a tab designed in the dimensional ranges set forth above excellent impedance matching is obtained for coupling to conductive line portions having a width in the range from 6 .020 to .025". The high permittivity substrate may preferably be formed of an alumina oxide ceramic of either 96% or 99.5% A1 0 for example. The thickness of the ground plane 20 may preferably lie in the range from In one typical embodiment lying within the dimensional ranges set forth above, the impedance is found to be 50 ohms. As shown in FIG. 5, the voltage standing wave ratio over an operating frequency range from DC. to 12 gigacycles as shown by curve 30, is well below 1.10. The curve 31 represents the standard VSWR requirements-curve 30 is clearly below minimum requirements over the entire frequency range.

FIGS. 6 and 7 show alternative embodiments of the launcher structure. FIG. 6 shows one embodiment in which the threaded member 12 is substantially cylindrical shaped and is not provided with a flange portion. The mounting frame 40 is comprised of a base portion 40a supporting circuit 18 and having an upwardly directed mounting portion 40b provided with a suitable opening 400 for press fitting the left-hand end of threaded member 12 so that the tab 15d makes firm surface contact With a conductive surface of the printed circuit.

As an alternative arrangement to the press fitting the threaded member 12 may be soldered to the mounting frame which is an insulating material such as, for example, glass, by providing solder around the periphery of threaded member 12 to form a good glass-to-metal seal in the region 41.

FIG. 7 shows still another alternative embodiment wherein the threaded member 12 is provided with a mounting flange 23 which is set inwardly from the extreme left-hand end of threaded member 12 by a distance D. The mounting frame, which may be any suitable insulating material such as, for example, glass, has an upwardly extending portion 40b joined to the base portion 404: which is provided with suitable openings for receiving threaded fasteners 17 and 23a. As was previously described with respect to FIG. 2, either of the embodiments of FIGS. 6 and 7 may be provided with an insulating clamping plate 22 which bears down upon the upper surface of tab 15d to further insure good pressure contact between the tab and the associated printed circuit 18.

The left-hand portion 12d of the threaded member assembly 12 shown in FIG. 7, is in actuality the internally mounted sleeve which is formed of a suitable dielectric material such as, for example, Teflon. The remainder of the threaded member may, for example, be formed of stainless steel. The center conductor in one preferred embodiment may be a gold-plated beryllium copper alloy.

It can be seen from the foregoing description that the present invention provides a novel launcher for use in coupling coaxial lines to non-symmetrical ground plane or microstrip line assemblies wherein design and packaging is greatly simplified by providing an in-line arrangement between microstrip and in-line assemblies; wherein the coupling and secure fastening between coaxial and microstrip line assemblies is simple and sure; wherein excellent impedance matching and extremely low VSWR is achieved over an operating frequency range from DC. to 12 gigacycles, which characteristics are not obtainable through conventional assemblies presently inuse and wherein the need for providing additional circuitry within the micnostrip line for balancing is completely eliminated.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.

What is claimed is:

1. A coupler for use in connecting a coaxial line to a microstrip line comprised of an insulating substrate having a circuit comprised of at least a strip conductor positioned near the edge of one surface and a single ground plane provided on the opposite surface to form a nonsymmetrical ground plane assembly; the improvement being characterized by providing a coupler comprised of a flat conductive member having a central Opening and a cylindrical shaped conductive portion extending outwardly from one side of said member to communicate with said opening;

said conductive portion including means for threadedly engaging a complementary member of a coaxial line;

a cylindrical shaped insulating sleeve being provided in said opening;

a conductive pin fitted within said insulating sleeve and having means at a first end of said pin for providing electrical coupling to a coaxial line;

the opposite end of said pin being provided with a tapered portion;

said tapered portion abruptly terminating in a substantially fiat surface forming a frusto-conical configuration;

a flat tab portion extending outwardly from and integrally formed with said pin;

said non-symmetrical ground plane assembly being positioned to abut the confronting surface of said first member opposite said one side of said member, which confronting surface is substantially coplanar with said pin fiat surface;

said tab lying outside of said insulating sleeve and having a first surface engaging the strip conductor;

said coupler providing an in-line connection between the coaxial line and the circuit.

2. The coupler of claim 1 wherein said conductive member is provided with a first group of apertures;

a second substrate being provided beneath said ground lane;

fastening means passing through said apertures and threadedly engaging said second substrate to secure said assembly to said coupler.

3. The coupler of claim 2 wherein the internal dimension of said apertures are greater than the external dimension of the fastening means passing therethrough to facilitate proper alignment of said tab and said strip conductor to allow for adjustment of contact pressure between said tab and said conductor.

4. The coupler of claim 3 further comprising a block of insulating material positioned above the first surface of said substrate and having a first surface engaging said tab and a second surface adjacent said first surface engaging the confronting surface of said member;

said member being provided with a second group of apertures;

second fastening means passing through said second group of apertures and threadedly engaging said block to secure said block to said member and to cause said block to firmly press said tab into engagement with said strip conductor.

5. The coupler of claim 4 wherein the internal dimension of said second group of apertures are greater than the external dimension of the second fastening means passing therethrough to allow for adjustment of contact pressure between said tab and said conductor.

6. The coupler of claim 1 wherein said pin is a solid one-piece conductive member;

the length and angle of taper of said tapered portion being selected to provide excellent impedance matching of the circuit assembly and coaxial line over a broad operating frequency range.

7. The coupler of claim 6 wherein said tab is symmetrically aligned relative to the longitudinal axis of said pH].

8. The coupler of claim 1 wherein the flat surface of said frusto-conical configuration is substantially coplanar with the confronting surface of said member.

9. The coupler of claim 1 wherein the length of said tapered portion is in the range from .010" to .040 and the angle of said taper is in the range from 8 to 36.

10. The coupler of claim 1 wherein the width of said tab is in the range from .018" to .022" and the thickness of said tapered portion lies in the range of .0275" to .0405".

References Cited UNITED STATES PATENTS 2,654,842 10/1953 Engelmann 33384(M) 2,721,309 10/1955 Seidel 33384(M) 2,749,524 6/1956 Derosa et al. 333-84(M) 2,825,876 3/1958 Le Vine et a1 33384(M) 2,968,012 1/1961 Alstadter 333-73(S) 2,990,523 6/1961 Jacques 33384(M) 3,013,227 12/1961 Jordan 33384(M) 3,118,119 1/1964 Leach 333-97X 3,201,722 8/1965 May et al. 333-84(M) 3,325,752 6/1967 Barker 333-34 FOREIGN PATENTS 1,159,756 8/1960 France 33384(M) OTHER REFERENCES Levy, R., New Coaxial-to-Stripline Transformers Using Rectangular Lines Ire. Trans. on Microwave Theory & Techniques, MTT 9, 1961, May, pp. 273274.

HERMAN KARL SAALBACH, Primary Examiner W. H. PUNTER, Assistant Examiner US. Cl. X.R. 

